The field of the present invention relates in general to vacuum processing of workpieces. More particularly, the field of the invention relates to systems and methods for low contamination, high throughput handling of workpieces including processing at a pressure different from atmospheric. Examples of such workpieces might include semiconductor wafers or flat panels for displays for which vacuum processing is usually required.
The increased cost for semiconductor manufacturing equipment and factory floor space has driven equipment vendors increasingly to compete on the productivity of their products and thus to have to increase the number of workpieces, such as wafers, that can be processed in any piece of such equipment per hour (throughput). There are three central factors that determine workpiece throughput: the time spent actually processing the workpieces (e.g. removing photoresist, implanting ions, etc.), the number of workpieces that can be simultaneously processed, and the amount of time that elapses between removing processed workpieces from a processing chamber and inserting unprocessed workpieces into the chamber.
In some conventional workpiece processing systems, there may be a significant delay between the time when processed workpieces are removed from a process chamber and the time when the new unprocessed workpieces are provided to the process chamber. For instance, some systems use a single robot arm to remove and insert workpieces. The robot arm must first align with the processed workpiece, remove the processed workpiece from the processing chamber, move to align with a storage area for processed workpieces (which may involve a 180 degree rotation), deposit the processed workpiece, move to align with a storage area containing unprocessed workpieces, retrieve an unprocessed workpiece, move to align with the processing chamber (which may involve a 180 degree rotation) and deposit the unprocessed workpiece in the processing chamber. The cumulative time required for all such steps may be large resulting in a substantial delay between the time when a processed workpiece is removed from the processing chamber and the time when a new unprocessed workpiece is provided to the processing chamber. In addition, each time that a batch containing a given number of workpieces is processed, these workpieces must be removed through a load lock to transit the pressure differential between atmosphere and process pressure and a new batch must be loaded into the processing environment. The time required for removing and loading batches and for pressurizing or evacuating the load lock also decreases throughput.
One system that has been designed to overcome some of the disadvantages of conventional systems is the currently available Aspen(trademark) system available from Mattson Technology, Inc. which is used to process semiconductor workpieces. In the current Aspen(trademark) system, a workpiece handling robot has two pairs of workpiece support paddles facing in opposite directions as shown in FIG. 1. Two new workpieces are loaded on the paddles on one side of the robot. Then two processed workpieces are removed from the process chamber on the paddles on the opposite side of the robot. The robot rotates once and then deposits the new workpieces in the process chamber and puts the processed workpieces back in the cassette which may hold from 13 to as many as 26 workpieces. Once a cassette of workpieces is processed, the cassette is removed and a new cassette is provided through the load lock mechanism shown in FIG. 2. As shown in FIG. 2, a rotation mechanism is used to exchange cassettes quickly in an outer load lock indicated at 202.
Another system designed to overcome some of the disadvantages of conventional systems is shown in FIGS. 3A and 3B and is described in U.S. Pat. No. 5,486,080. In this system two separate robots 62 and 64 move independently of one another to transport workpieces between an implantation station 25 and load locks 22a and 22b. An intermediate transfer station 50 is used to transfer the workpieces. FIG. 3B is a workpiece path diagram showing the transport steps used to move workpieces in the system. While a first robot transports an unprocessed workpiece from the transfer station 50 to the implantation station 25, a second robot transports a processed workpiece from the implantation station 25 to one of the load locks 22a or 22b. While one load lock is being used for processing, the other load lock can be pressurized, reloaded and evacuated.
While the above systems improve throughput and decrease down time for pressurizing and evacuating load locks, reductions in system size, complexity, and cost while maintaining or improving throughput are still needed. For instance, the system of FIGS. 3A and 3B uses two separate robots and a transfer station all of which take up space. However, it is desirable to decrease the size of workpiece processing systems to the extent possible, because the clean room area used for the system is very expensive to maintain. In addition, separate drive mechanisms which may be used for the two robots would be expected to be more complicated and expensive than a system that employs only one drive mechanism.
In addition to throughput, size, complexity and cost, a fundamental constraint on workpiece handling systems is the necessity to avoid contaminating workpieces. Very small amounts of contaminants, such as dirt or dust can render a workpiece unusable and the size and number tolerance for particulate contaminants continues to decrease as workpiece geometries decrease. Workpiece processing equipment may introduce contaminants in a variety of ways. For example, particles may be shed when two pieces of machinery rub or touch. It is important to minimize the exposure of the workpieces to such contaminants during handling and processing.
It is a particular challenge to design doors that minimize particles generated by friction. Doors open and close to allow workpieces to pass between the ambient (usually a clean room environment) to a sealed (and possibly evacuated) chamber or between two chambers. Opening and closing the doors may involve mechanical mechanisms that create particles or may generate particles when two surfaces are pushed together to close the door. It is desirable to decrease the number of particles generated by such doors to reduce the likelihood of contaminating workpieces. In addition to avoiding contamination, it is desirable in many instances to use a door that does not occupy much space, thereby reducing the overall size of the system and conserving valuable clean room space.
In summary, there is a need for a workpiece handling system with high throughput but that does not entail relatively complicated or expensive mechanisms, or mechanisms that occupy a relatively large amount of space. There is a further need for a workpiece processing system with reduced particle generation and workpiece contamination. Without limiting the foregoing, there is a need for door assemblies for use in such systems which reduce the potential for contamination and occupy a relatively small space. Preferably a workpiece handling and processing system would satisfy all of the foregoing needs.
Aspects of the present invention provide a workpiece processing system including multiple load locks, a workpiece transfer chamber and one or more process chamber(s). In these aspects of the invention, the core of the system consists of the aforementioned multiple load lock stations, which may be stacked vertically and act as buffers between a workpiece handler at atmospheric pressure and another workpiece handler at another pressure typically closer to the pressure at which the processes are done. In another embodiment each load lock may function independently from the other(s). Hence, one may be open to atmosphere where a handler unloads or reloads workpieces while other(s) operate, for example, in partial vacuum, allowing a vacuum handler to supply workpieces to and from the process chamber(s). Additionally, the load locks may provide the capability to cool post process workpieces prior to or during their pressure transition from the reduced pressure of the load lock to atmospheric pressure. This functional independence makes such a system capable of providing a steady supply of pre-processed workpieces for the vacuum handler thus achieving high throughput in nearly continuous workpiece processing.
In another embodiment, a controlled mini-environment can be created on the atmospheric side of the load locks to provide a clean, particle free volume for loading or unloading workpieces. Air filtration systems and/or laminar flow hoods can be incorporated for the purpose of contamination control. Multiple workpiece-holder docking stations can be mounted to the enclosure, creating a supply of pre-processed workpieces to the system.
In another embodiment, a robotics handler can operate in the mini-environment and bring workpieces from their holders (which may be called cassettes) to the load locks and back again. This handler can utilize any combination of compound or individual rotational, vertical, and horizontal movements to selectively align with the workpiece cassettes or load locks for the purpose of transferring workpieces. The robot handler can have two sets of paddles, or other devices intended for retaining the workpieces during said transport. One set may consist of multiple, vertically stacked paddles, while the other may be a single paddle situated below the others. Each set is capable of independent or dependent linear motion such that any combination of the two can be used to transport workpieces to and from the load locks. Additional components can be mounted to the robot, or be made accessible in the mini-environment. These stations could provide operations such as workpiece identification or any other pre- or post-process inspection.
In another embodiment, a linear door mechanism may be used to seal one doorway of each load lock. An extractable door plate contained in a housing may be extended against the doorway for sealing or retracted for unsealing. The door plate and housing may then be raised or lowered to provide access for workpieces to pass through the doorway. If load locks are positioned above one another, the door of the upper load lock might raise when opened and, conversely, the lower door might drop to provide a pathway for workpiece transfer.
In another embodiment, dual or multiple load locks can be stacked vertically to minimize the system footprint. Each load lock may contain shelves adjacent to which workpieces can be placed and staged. These shelves may be situated such that workpieces are contained next to and on top of one another. Workpiece temperature could be controlled through thermal contact with the shelves which may be heated or cooled by gaseous conduction and radiation. Gases might also be directed over the workpieces, prior to or after processing, to achieve desired temperatures.
In another embodiment, a rotational door may be used to seal the other doorway of each load lock. This door may be extended against the doorway for sealing or retracted for unsealing. Once decoupled from the doorway, the door may rotate up or down to allow workpieces to pass through. The door of the upper load lock may rotate upward when opened and the lower load lock door may rotate downward. The compactness of the door""s operation allows for vertically stacked load locks occupying minimal space.
In one embodiment a robot handler residing in a central transfer chamber, with pressure closer to process chamber pressure than atmospheric pressure may be utilized to transport workpieces from the load locks to the process chamber(s) and back to the load locks after processing. Such duties may be shared by two robotic arms utilizing common compound or individual vertical and rotational movements, but acting independently when extending or retracting to pick or place workpieces. Additionally, two or possibly more workpieces may be located side by side on paddles or other devices fixed to each robot arm. Furthermore, the robots may operate in an over/under fashion to reduce their geometrical profile and minimize the transfer time of post- and pre-processed workpieces. The robot arm structure can be made to avoid any bearing surfaces passing directly over a workpiece and thus helping ensure cleaner, lower-particle-on workpiece contamination during operation.
In another embodiment, a slit door could be used to isolate the process chamber environment from that of the transfer chamber. Such a door could work utilizing vertical motions to allow passage of workpieces through the process chamber doorway. Small horizontal motion could be used to seal or unseal the door from the doorway. Both motions allow for a very compact door and contribute to minimizing the footprint of the system. Such a door could be made to seal off positive pressure in the process chamber while the transfer chamber operated at negative pressure. In another embodiment, a process chamber could be serviced at atmospheric pressure while the transfer chamber remained at partial or near-vacuum.
In another embodiment, the transfer chamber could be designed to dock three or more process chambers, each capable of processing two or more workpieces side by side. Each process chamber could be designed as a modular entity, requiring a minimum amount of effort to mount to and communicate with the main transfer chamber and its elements. Additionally, multiple process chambers mounted to the transfer chamber might each provide the same or different process capability.
In another embodiment, pre- or post-process stations could be located in the transfer chamber and made accessible to the vacuum robot handler. Examples of such processes include, but are not limited to, preheating or cooling of workpieces and workpiece orientation and alignment.